The long-term objective of this project is to study the biological function of the mammalian ortholog of Drosophila rdgB (mrdgB) in the visual process. Mutations of rdgB cause light-enhanced retinal degeneration in flies. The MrdgB and RdgB proteins share high degrees of structural and functional conservation. When mrdgB is expressed in rdgB mutant flies, it suppresses the light-enhanced retinal degeneration and restores normal ERGs. This finding is surprising given the significant morphological and biochemical differences between fly and vertebrate eyes, and suggests the possibility of functional similarities between the species that were not previously appreciated. The biological functions of either rdgB or mrdgB are not yet known. In order to begin to understand the role of mrdgB in the mammalian visual system, several experiments are proposed. First, the developmental expression pattern of mrdgB in the mouse eye will be characterized. Also, because rdgB exhibits phosphatidylinositol transferase (PIT) and calcium-binding activities, the MrdgB protein will be assayed to determine whether it also possesses these biochemical activities in vitro. The most direct method to assess mrdgB function in the mammalian retina is to disrupt its function. Therefore, the main focus of this project will be to generate mrdgB knock-out mice. This will be achieved by targeted gene disruption in murine embryonic stem cells. Another effective way to study the function of a protein is to isolate and characterize proteins with which it interacts. To achieve this, the yeast two-hybrid system will be used to characterize proteins that interact with MrdgB. Hopefully, these studies will provide new insights into the biology of vision and increase our understanding of human retinal degeneration.